Harmonic balancer pinning location
Thread Starter
Heel & Toe
Joined: Apr 2026
Posts: 22
Likes: 1
Harmonic balancer pinning location
Hi, I’m installing a new harmonic balancer right now. I chose to go with the summit c2501 which has a key way. I’m planning on pinning it (I figured I might as well since I’m already down there and I found a pinning kit for pretty cheap) however I had some questions: where on the balancer should I pin it, I’ve heard both thru the existing keyway, or directly opposite to it (seems to be the more accepted option), or does it matter at all. Should I fill the keyway with silicone or something (also heard it both ways)? And any other tips or things I should keep in mind while pinning or for the rest of the job in general? Thank you for your time.
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
Hi, I’m installing a new harmonic balancer right now. I chose to go with the summit c2501 which has a key way. I’m planning on pinning it (I figured I might as well since I’m already down there and I found a pinning kit for pretty cheap) however I had some questions: where on the balancer should I pin it, I’ve heard both thru the existing keyway, or directly opposite to it (seems to be the more accepted option), or does it matter at all. Should I fill the keyway with silicone or something (also heard it both ways)? And any other tips or things I should keep in mind while pinning or for the rest of the job in general? Thank you for your time.
Race Director
Joined: Oct 2004
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My question is why did you buy the keyed version?? My suggestion would be to ask the manufacturer. IMHO, the removed metal for the keyway throws the balance off from the start. When the key is installed, it puts the weight back, somewhat rebalancing the unit. Without that key, and if you pin it opposite the keyway, you'll throw the balance off even more. Because you've added weight 180° from where you've already removed weight. It may, or may not matter considering the weight changes are close to the crank centerline. Honestly, if you can return the balancer and exchange it for a non-keyed version, that's what I would do..
Last edited by grinder11; May 3, 2026 at 11:32 AM.
Thread Starter
Heel & Toe
Joined: Apr 2026
Posts: 22
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I picked up the summit one because it was sfi rated, and I figured since I’m not sure my plans for the car down the line I might as well go with one that’s more robust. However, it seems all sfi rated balancer, or most balancers that aren’t oem style (which I heard to stay away from due to having a higher chance of the wobbling issue returning which is why I’m replacing mine to begin with) have a keyway in them. I’ve looked at the three brands that are commonly recommended (summit, ati, and PowerBond) and all three have keyways in them.
Tech Contributor
Joined: Jan 2007
Posts: 19,450
Likes: 1,155
From: Dyer, IN
I picked up the summit one because it was sfi rated, and I figured since I’m not sure my plans for the car down the line I might as well go with one that’s more robust. However, it seems all sfi rated balancer, or most balancers that aren’t oem style (which I heard to stay away from due to having a higher chance of the wobbling issue returning which is why I’m replacing mine to begin with) have a keyway in them. I’ve looked at the three brands that are commonly recommended (summit, ati, and PowerBond) and all three have keyways in them.
Thread Starter
Heel & Toe
Joined: Apr 2026
Posts: 22
Likes: 1
My choices were mainly driven by discussions on this forum, and looking at the part specifications:
https://www.corvetteforum.com/forums...to-choose.html
https://www.corvetteforum.com/forums...r-pinning.html (doesn't seem like there's a clear consensus here on where to pin)
https://www.corvetteforum.com/forums...-balancer.html
I just wanted a second opinion on where to actually pin the balancer, but it seems like there isn't much of an issue with the keyway being there based on what most people are saying. and it seems like pretty much every balancer other than the oem ones (which based on what I've seen on the forum people have been told to stay away from), has a keyway that I haven't seen anyone saying will cause any issues with leaking or imbalance (and to my understanding the c5's engine is internally balanced, so the balancer itself shouldn't affect that at all, though I may be wrong on that).
https://www.corvetteforum.com/forums...to-choose.html
https://www.corvetteforum.com/forums...r-pinning.html (doesn't seem like there's a clear consensus here on where to pin)
https://www.corvetteforum.com/forums...-balancer.html
I just wanted a second opinion on where to actually pin the balancer, but it seems like there isn't much of an issue with the keyway being there based on what most people are saying. and it seems like pretty much every balancer other than the oem ones (which based on what I've seen on the forum people have been told to stay away from), has a keyway that I haven't seen anyone saying will cause any issues with leaking or imbalance (and to my understanding the c5's engine is internally balanced, so the balancer itself shouldn't affect that at all, though I may be wrong on that).
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Joined: May 2025
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From: Howard, Ks.
[QUOTE=grinder11;1609619717]My question is why did you buy the keyed version?? My suggestion would be to ask the manufacturer. IMHO, the removed metal for the keyway throws the balance off from the start. When the key is installed, it puts the weight back, somewhat rebalancing the unit. Without that key, and if you pin it opposite the keyway, you'll throw the balance off even more. Because you've added weight 180° from where you've already removed weight. It may, or may not matter considering the weight changes are close to the crank centerline. Honestly, if you can return the balancer and exchange it for a non-keyed version, that's what I would do..[/QUOTE When I replace mine, I will use a "broaching cutter" on mine. Press on the balancer, Drive the appropriate broaching cutter in and cut a keyway in the end of the crankshaft. Blow out or vacuum out cuttings and drive in key. This method is used on Harley Davidson flywheels to index shafts.
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That is VERY interesting, harleydoctor. Before you make that leap, I'd be absolutely certain someone makes that special broach for our V8s. Personally, I've never seen or heard of anyone doing this on a V8. That doesn't mean that it's not available. I don't like the idea of forcing steel chips into the engine. You'll never get every one out with air or vacuum. When I ran a keyed balancer, it was a Woodruff key slot, and key. If I were the OP, I'd exchange it, and get a keyless balancer. Then he could pin it wherever he wants, if needed, with no internal chips...
Last edited by grinder11; May 5, 2026 at 09:10 AM.
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I picked up the summit one because it was sfi rated, and I figured since I’m not sure my plans for the car down the line I might as well go with one that’s more robust. However, it seems all sfi rated balancer, or most balancers that aren’t oem style (which I heard to stay away from due to having a higher chance of the wobbling issue returning which is why I’m replacing mine to begin with) have a keyway in them. I’ve looked at the three brands that are commonly recommended (summit, ati, and PowerBond) and all three have keyways in them.
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Joined: May 2025
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From: Howard, Ks.
That is VERY interesting, harleydoctor. Before you make that leap, I'd be absolutely certain someone makes that special broach for our V8s. Personally, I've never seen or heard of anyone doing this on a V8. That doesn't mean that it's not available. I don't like the idea of forcing steel chips into the engine. You'll never get every one out with air or vacuum. When I ran a keyed balancer, it was a Woodruff key slit, and key. If I were the OP, I'd exchange it, and get a keyless balancer. Then he could pin it wherever he wants, if needed, with no internal chips...
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Joined: May 2025
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From: Howard, Ks.
The keyway cut in the crank would never extend into the engine cavity, a wad of grease would hold any loose chips to be vacuumed out. This is a slow hammering process not a machine operation. ten-minute job max though.
Drifting
Joined: Sep 2022
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Put a glob of silicone in the end of the keyway slot, pin it opposite the keyway and stop worrying so much about it, it'll be fine.
Balance issue is non-existent, tiny amount of weight is too close to crank centerline to be an issue.
Balance issue is non-existent, tiny amount of weight is too close to crank centerline to be an issue.
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Hi, I’m installing a new harmonic balancer right now. I chose to go with the summit c2501 which has a key way. I’m planning on pinning it (I figured I might as well since I’m already down there and I found a pinning kit for pretty cheap) however I had some questions: where on the balancer should I pin it, I’ve heard both thru the existing keyway, or directly opposite to it (seems to be the more accepted option), or does it matter at all. Should I fill the keyway with silicone or something (also heard it both ways)? And any other tips or things I should keep in mind while pinning or for the rest of the job in general? Thank you for your time.
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Hey man we've been pinning cranks for many years now. Just use some RTV in the square hole to prevent any oil leaks. Drill your round hole anywhere that is not in the square hole and you will be fine. No balance issues to worry about either. We also install and recommend those C2501 units.
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Broaching cutters come in different widths, with 3/16 & 1/4 inch being the most common, but all widths are available. Insert the broach in the balancers keyway and hammer in until desired depth is achieved. I became aware of this while working at Truett & Osborne Cycle in Wichita , Ks. where we manufactured flywheels (aka crankshafts) in various strokes up to 5 1/4 inch torque monsters. The right hand crank pin (pinion shaft) had to be indexed to the crank for camshaft timing. Also the connecting rod pin was also keyed to align oiling hole. When I change out my balancer on my 2K I will be cutting a keyway in the crank.
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From: Howard, Ks.
As a retired Tool & Diemaker, I'm well aware broaches come in many sizes. Used them hundreds of times over 41 years. I still think he should exchange the balancer. As my career ended, tooling quality became very questionable. I once had a 5/8" drill split in 2 perfect halves. It was an investment cast piece of junk, made in a middle east country. It would be a PITA to have a substandard broach break while hammering on it. Also, do you know if the LS balancers use metric or SAE keyways? Just asking...